PowerBoon power button

I've just bought a second-hand TiBook. Works basically ok. But pressing the power button usually does not turn it on. Pressing Command-Control-Power does start it ok. So I am not too worried, but would still like to know the cause and how easy it is to return to standard use.

My own theory is that this is caused by a dead back-up battery. It seems quite likely that this battery is dead on a five-year-old machine.